The invention relates to a measuring system for determining the shape and length of a surface line of a body with a freely movable measuring instrument, which is equipped with a measuring device for measuring the length of a displacement path of the measuring instrument along the surface line and a measuring device for determining angular changes of a measuring axis of the measuring instrument with respect to a predetermined reference axis, with a data transfer device to a computer and a computer which processes the path and angle measurements of the two measuring instruments and generates a representation of the surface line.
Such measuring systems are in particular applied for acquiring and scanning the shape and length of body contours and of ranges of motion in the case of articulated bodies, in particular human bodies. Of particular interest are the acquisition of the shape and length of the course of the vertebral column and measuring for checking its mobility, but also for measuring the course of motions on other joints, such as, for example, hip or knee joints. A measuring system of this type is known, for example, from DE 40 90 228 C1, in which different application feasibilities in the area of measurements on the vertebral column are also described. In this known system, a freely movable measuring instrument is available, which is:connected to a computer for evaluating and representing the data. In the movable measuring instrument a measuring device is available for measuring the length of the displacement path of the measuring instrument, and specifically an electric path-measuring sensing element. This path measuring device includes rollers or cylinders, which, during the displacement of the measuring instrument, track along the surface or line to be measured and means, known per se, for converting this tracking motion into electric signals, for example via an incremental displacement transducer. The measuring instrument further includes also an angle measuring device in the form of a vertical pendulum device. This vertical pendulum device is developed such that it can be applied in two positions pivoted by 90xc2x0. This allows in a first measuring process by tracing the surface line with the movable measuring instrument determining curvatures in one direction and by repeating the tracing process and resetting the vertical pendulum device by 90xc2x0, curvatures of the surface line in a plane at right angles to [the first plane]. To determine the curvature and shape of the surface line, at specific points, or intervals of the path of this surface line, the corresponding angular deviations via the vertical pendulum and on that basis to determine the curvature of the surface line. The vertical pendulums applied for angle measurements represent relatively sensitive, and also correspondingly expensive, measuring instruments, and, in the commercially available implementations, they also have only a limited angle measuring range. If, in the case of measurements on the human body, for example in patients with back complaints, measurements must be carried out on the standing and also on the lying body, these different measurements require a resetting of the measuring instrument, for example of the vertical pendulum device, for the particular position of the patient. As a consequence, the measuring electronics must also be newly initiated and the originating point of the measurement must be started accordingly. This is time consuming and can also lead to discrepancies of the measuring results and to errors, since movements in the interim by the patient cannot be excluded.
A further measuring system for acquiring the back contour of a human being is known from DE 44 02 562 A1. In this system a vertical pendulum is also applied for angle measurements in the movable measuring instrument. While this vertical pendulum has an increased angle measuring range, it entails, however, additionally the disadvantage that vertical pendulums are sensitive measuring instruments with a complicated interior structure. They are therefore correspondingly expensive and also require careful handling and correct application. During the measurements the vertical pendulum must be oriented as must as feasible in a vertical plane since otherwise the damping could falsify the measurement results. With too great a deviation from the vertical plane, measurements can even become impossible.
In practice difficulties are therefore repeatedly encountered since the measured object on which the shape and length of a surface line is to be acquired, must be moved into a position which corresponds to the permissible measuring range of the measuring system. In particular in the case of measurements on the human body and wherever measurements or sequences of measuring series must be carried out rapidly, this makes the course of measurement difficult. The known measuring systems therefore require corresponding training and practice in the application. Even with correspondingly trained operators the time expenditure for carrying out measurements is, to some extent, still considerable, and, in particular, resetting the angle measuring device and the respective initialization are time-consuming.
The objective of the present invention is to provide a measuring system or a measuring instrument, with which the acquisition of shape and length of surface lines of a body in a plane over an angular range from 0 to 360xc2x0 is possible, with changes of position of the measuring instrument or with changing measuring processes no initialization and calibration of the measuring instrument is necessary, the measuring device for determining the angular changes in [three-dimensional] space is structured simple and freely movable, and the course of the surface line in the same measuring process can be determined with respect to two measuring surfaces, oriented at right angles to one another, or as a space vector.
This object is attained through the features defined in the claims to and forming part of this application.
In the measuring system according to the invention the movable measuring instrument is equipped with a measuring device, known per se, for measuring the length of a displacement path along a surface line, as is described in prior art. In combination with this length measuring device, known per se, the measuring device for determining angular changes of a measuring axis of the measuring instrument, is developed with two acceleration sensors. Application of acceleration sensors for determining angular changes of the measuring device yields the advantage that sensors can be employed which have a precisely defined measuring axis and, additionally, no movable parts exist which must be supported such that they are pivotable about an axis or are equipped with damping elements. This significantly simplifies the structure of the measuring device for determining angular changes and the susceptibility to malfunction is considerably reduced. The acceleration sensors proposed for use, are sensors which normally are applied to determine accelerations and decelerations of moving objects in the direction of their measuring axis. But such sensors, known per se, also have the property that even in the stationary state, i.e. without a motion component in the direction of their measuring axis, they output measuring signals with angular changes of the measuring axis. This effect can be traced back to the normal gravitational force, or acceleration due to gravity, which always acts on the sensor. If an acceleration sensor is oriented such that the measuring axis is parallel to the gravitational axis, the full acceleration due to gravity acts on the measuring element of the acceleration sensor. If the measuring axis of the acceleration sensor is precisely at right angles to the gravitational axis, the measuring element of the acceleration sensor is not deflected and no component of the acceleration due to gravity acts in the direction of the measuring axis. Depending on the angular position between 0 and 90xc2x0, the acceleration sensor generates different measuring signals, from which the angular position of the measuring axis of the acceleration sensor relative to the gravitational axis can be derived. Known acceleration sensors comprise a sensor and an integrated circuit which is normally developed as a closed unit with a power connection and a signal output. However, the dependence of the signals output by the acceleration sensor is not a linear function of the angle but rather the sensitivity in the proximity of 90xc2x0 with respect to the gravitational axis is greatest and in the range, in which the measuring axis is moved into a parallel position with the gravitational axis, it is low.
A further advantage is obtained if in one measuring plane two acceleration sensors are disposed whose measuring axes lie in this common plane and are disposed at right angles to one another. If the output signals of these two acceleration sensors are linked, a unique assignment to a specific angle relative to the gravitational axis is obtained and simultaneously high precision since one of the two sensors is always effective in the range of high sensitivity. Since the two acceleration sensors are not dependent on a rotational axis, but their measuring axis can fundamentally be disposed in any desired manner in space, the advantage is obtained that the plane in which the two measuring axes of the acceleration sensors are disposed, can be oriented in the measuring instrument such that the measuring axis of the measuring device for the displacement path is also in this common plane. The output signals of the acceleration sensors are conducted to a transducer and such is connected across an interface and a data line with a computer, advantageously a personal computer. This data line can be formed by a cable, and an especially advantageous solution is obtained if the data of the transducer can be transferred wirelessly to the computer. This increases the free mobility of the measuring instrument, and it is readily handlable by the operating personnel.
By using a third acceleration sensor, in simple and advantageous manner a second measuring device for determining angular changes can be formed, thereby that this third acceleration sensor is combined with one of the two sensors of the first measuring device for determining angular changes, to form a second measuring device. The measuring axis of this third acceleration sensor is disposed in a plane which is at right angles to the plane formed by the measuring axes of the two first acceleration sensors. Thereby that two sensors each are combined to form a first and a second measuring device, angular changes can be detected in two planes perpendicular to one another. The measuring range extends from 0 to 360xc2x0 in each of the two planes since one of the sensors is always within the sensitive measuring range. Since the characteristic of the signal curve as a function of the angle of the measuring axis to the gravitational axis is known precisely, the angles can be determined with high precision and over the entire range. The measuring system according to the invention offers additionally the advantage that different models of acceleration sensors can be employed since their signal or measuring characteristic is known from the outset. Through the appropriate evaluation of the measuring signals in the computer with suitable software any desired angle in space in the X- as well as the Y- and the Z-axis can be determined. If needed, these measuring signals can also be converted into vectors. In connection with the measured values from the path measurement, the measured values from the angle measurement are used to represent the course of surface lines of a body.
To acquire the shape and length of a surface line of a body, for example the shape of the vertebral column of a human being, the measuring instrument is moved along the vertebral column or the surface line. The measuring device for measuring the length of the displacement path senses the corresponding displacement movement and, via the transducer, the corresponding measured values are transferred as data to the computer. At predetermined path and/or time intervals for this purpose, via the measuring devices for determining angular changes, the angles of inclination of the surface line are determined. From the data belonging to a specific measuring point the course of the surface line in the region of this measuring point is calculated and subsequently, based on the multiplicity of measuring points, the course of the total curve or the total surface line is determined. Such can subsequently, in a manner known per se, be represented or output on an output apparatus, such as a printer or a monitor, and can be made accessible to a viewer. During a movement process of the measuring instrument, intermediate states of the curve of the movement and final states can be determined and represented. The measuring system according to the invention does not require calibration in the starting position since, due to the measurement values of the sensors, it is always possible to determine precisely which positions are assumed by the measuring axes of the measuring instrument with respect to the gravitational axis. This facilitates considerably the course of measuring processes, for example on patients with back or joint complaints, since these are not forced to assume a specific measuring position. For standard measurements it is certainly useful to start from at least one or several approximate normal positions. This facilitates the comparison of measuring processes with one another and also the evaluation of the displayed results. With sufficient experience of the operating personnel and the use of suitable software, the measuring system according to the invention also makes possible measurements in any position, i.e. the application range of this measuring system is considerably expanded. In spite of this expansion of the application range, the measuring instrument is easy to handle and not subject to malfunctions.
Disposing an input apparatus with at least one control key on the movable measuring instrument offers the further advantage that the operatability is improved thereby that control functions for the data processing in the PC can be actuated via these control keys and, for example during the measuring processes, the control keyboard proper of the computer is replaced by these control keys. Facilitation of the work resulting therefrom is considerable and permits working fast and precisely. A further improvement is obtained by disposing a display arrangement on the measuring instrument. This display arrangement can be formed by a light-emitting. diode (LED) or by another arrangement, known per se, such as a liquid crystal display (LCD). A light-emitting diode could visually display certain operating states. When using a liquid crystal display the expanded capability is obtained for displays in the form of symbols, numerals or text. This display arrangement makes it possible for the operating personnel to direct their entire attention to the measuring process and the measuring instrument since all operation messages can be displayed on the measuring instrument. This also contributes to additional ease and acceleration of the measuring process.